On two methods using magnetometer-array data for studying magnetic pulsations

Ground magnetometer data have been providing important knowledge of magnetic pulsations (or ULF waves) for more than a hundred years. With the advance of modern technologies, the accuracy of measurements is constantly improving. In addition, more arrays of magnetometer stations have been established. However, the usage of magnetometer arrays for studying magnetic pulsations has not been fully exploited. In this study, two recently developed methods for pulsation analysis are introduced. The first method involves an inversion technique that requires the observations from a chain of magnetometer stations located on a same latitude. This method can estimate several physical quantities related to the pulsation amplitude, namely the magnitude of the wave “event”, the local time distribution, and the ground conductivity effect. The second method dubbed “the cross-phase technique” calculates the phase-difference spectrum of the signals measured at two closely separated stations on a same meridian. This technique has been found to be successful in “observing” the eigenfrequencies of magnetospheric field lines. It also provides an interesting opportunity to compare the field line resonance theory with the observations in detail.